Hydrocarbon adsorbent

ABSTRACT

To provide a hydrocarbon adsorbent having high hydrocarbon adsorbing properties even after exposed to a high temperature/high humidity reducing atmosphere. 
     A hydrocarbon adsorbent, which includes a FAU type zeolite having a lattice constant of at least 24.29 Å and containing copper. Such a hydrocarbon adsorbent may be used for a method for adsorbing hydrocarbons to be exposed to a high temperature/high humidity environment, and may be used particularly for a method for adsorbing hydrocarbons in an exhaust gas of an internal combustion engine, such as an automobile exhaust gas.

TECHNICAL FIELD

An exhaust gas discharged from an internal combustion engine used forvehicles such as automobiles and ships contains a large quantity ofhydrocarbons, and the hydrocarbons discharged from the internalcombustion engine are clarified by a three way catalyst. However, thethree way catalyst requires a temperature environment of at least 200°C. to function, and in a temperature range in which the three waycatalyst does not function, for example, at the time of cold start, thehydrocarbons are adsorbed in a hydrocarbon adsorbent, discharged fromthe adsorbent at a temperature range at which the three way catalyststarts functioning, and decomposed and clarified by the three waycatalyst.

The temperature of an automobile exhaust gas reaches 900° C. or higherdepending upon the engine operation state. Further, the exhaust gascomposition varies depending upon the operation state. The air fuelratio (air/fuel mixture) when oxygen and a fuel mixture in the mixed gasreact with each other without any excess nor deficiency is calledtheoretical air fuel ratio. In actual operation, the fuel does notalways burn at the theoretical air fuel ratio, and lean burn with an airfuel ratio higher than the theoretical air fuel ratio and rich burn withan air fuel ratio lower than the theoretical air fuel ratio are employeddepending upon the load state. The lean burn is burning at an oxygenconcentration higher than that of complete combustion of the fuelmixture, and the exhaust gas contains oxygen in an amount of from 3 to15 vol %, that is, in an oxidizing atmosphere. On the other hand, richburn is combustion with excess fuel, and the exhaust gas containsunburned hydrocarbons and is thereby in a reducing atmosphere.Accordingly, the hydrocarbon adsorbent is required to have high thermaldurability in oxidizing/reducing atmosphere.

As a method for adsorbing and clarifying hydrocarbons from an exhaustgas at low temperature, an adsorbing catalyst for purifying exhaust gascomprising zeolite with a SiO₂/Al₂O₃ molar ratio of from 50 to 2,000,such as mordenite, β-zeolite or ZSM-5 and containing at least oneselected from the group consisting of Pt, Pd and Rh (Patent Document 1),a molecular sieve having Ag supported (Patent Document 2) and ZSM-5zeolite comprising Cu ion-exchanged with at least one metal selectedfrom the group consisting of Co, Ni, Cr, Fe, Mn, Ag, Au, Pt, Pd, Ru, Rhand V (Patent Document 3) have been proposed.

Each of methods for adsorbing and removing hydrocarbons using suchadsorbents employs a system such that hydrocarbons contained in anexhaust gas are once adsorbed in the adsorbent at a low temperatureregion at the time of start of the engine, and the hydrocarbons desorbedfrom the adsorbent at a temperature at which the exhaust gas clarifyingcatalyst functions or higher, are clarified by a catalyst, and each ofthe conventional adsorbents is insufficient in durability in a hot andhumid environment particularly in durability at high temperature ofabout 900° C.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-H07-213910

Patent Document 2: JP-A-H06-126165

Patent Document 3: JP-A-H06-210163

DISCLOSURE OF INVENTION Technical Problem

It is an object of the present invention to provide a hydrocarbonadsorbent having high hydrocarbon adsorbing properties even afterexposed to a high temperature/high humidity reducing atmosphere.

Solution to Problem

The present inventors have conducted extensive studies on hydrocarbonadsorbents used to adsorb hydrocarbons mainly in an exhaust gas of aninternal combustion engine and their properties. As a result, they havefound a hydrocarbon adsorbent having high hydrocarbon adsorbingproperties even after exposed to a high temperature/high humidityreducing atmosphere by controlling physical properties of a FAUstructure zeolite.

That is, the present invention provides the following.

[1] A hydrocarbon adsorbent which comprises a FAU type zeolite having alattice constant of at least 24.29 Å and containing copper.

[2] The hydrocarbon adsorbent according to [1], wherein the FAU typezeolite has an average crystal size of at least 0.45 μm.

[3] The hydrocarbon adsorbent according to [1] or [2], wherein the FAUtype zeolite has a copper content of at least 0.5 wt % and at most 4.0wt %.

[4] The hydrocarbon adsorbent according to any one of [1] to [3],wherein the FAU type zeolite has an alkali metal content as calculatedas oxides of at most 1 wt %.

[5] The hydrocarbon adsorbent according to any one of [1] to [4],wherein the FAU type zeolite has a hydrogen consumption peak with a peaktop at a temperature of at least 300° C. and at most 500° C., in H₂-TRPmeasurement in a state after subjected to exposure treatment to areducing atmosphere at a temperature of at least 800° C. and at most1,000° C. and then to exposure treatment to an oxidizing atmosphere at atemperature of at least 400° C. and at most 600° C.

[6] The hydrocarbon adsorbent according to any one of [1] to [5],wherein the FAU type zeolite has, in ESR measurement, a spinconcentration of a least 1.0×10¹⁹ (spins/g) and a ratio of a peakintensity at a magnetic field of at least 260 mT and at most 270 mT to apeak intensity at a magnetic field of at least 300 mT and at most 320 mTof at least 0.25 and at most 0.50.

[7] A method for treating a hydrocarbon-containing gas, which uses thehydrocarbon adsorbent as defined in any one of [1] to [6].

Advantageous Effects of Invention

According to the present invention, it is possible to provide ahydrocarbon adsorbent having high hydrocarbon adsorbing properties evenafter exposed to a high temperature/high humidity reducing atmosphere.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating the relation between the lattice constantand the hydrocarbon adsorption ratio after reduction hydrothermaldurability treatment.

FIG. 2 is a graph illustrating the relation between the SiO₂/Al₂O₃ molarratio and the hydrocarbon adsorption ratio after reduction hydrothermaldurability treatment.

FIG. 3 is a graph illustrating the relation between the copper contentand the hydrocarbon adsorption ratio after reduction hydrothermaldurability treatment.

FIG. 4 illustrates H₂-TPR measurement results of Example 1.

FIG. 5 illustrates H₂-TPR measurement results of Comparative Example 3.

FIG. 6 illustrates ESR measurement results of Example 3.

DESCRIPTION OF EMBODIMENTS

Now, embodiments of the hydrocarbon adsorbent of the present inventionwill be described.

In an embodiment of the present invention, the hydrocarbon adsorbentcontains a FAU type zeolite. The FAU type zeolite is a zeolite having aFAU structure, and is preferably a crystalline aluminosilicate having aFAU structure. The FAU structure is framework type code defined as “FAU”by the International Zeolite Association (hereinafter sometimes referredto simply as “framework type code”). The structure may be confirmed by apowder X-ray diffraction (hereinafter sometimes referred to as “XRD”)pattern as described in Collection of simulated XRD powder patterns forzeolites, Fifth revised edition (2007).

The crystal structure of the FAU type zeolite comprises structural unitsof sodalite cages consisting of 4-oxygen rings and 6-oxygen rings, anddouble six-oxygen rings (hereinafter sometimes referred to as “D6R”),and has pores formed of 12-oxygen rings (hereinafter sometimes referredto as “12-oxygen ring pores”) formed of such structural unitsthree-dimensionally bonded. By the FAU type zeolite having the 12-oxygenring pores, it can adsorb even bulky hydrocarbons such as aromatichydrocarbons. Further, copper and aluminum constituting the structuralunits have strong interaction. In the FAU type zeolite, aluminumconstituting D6R and copper strongly interact with each other, wherebycopper is held in zeolite, mainly in the crystal structure, with ahomogeneously dispersed state, and the hydrocarbon adsorbing propertiesof the FAU type zeolite will hardly decrease.

In the embodiment of the present invention, the FAU type zeolite has alattice constant of at least 24.29 Å, preferably at least 24.30 Å. In aFAU type zeolite having a lattice constant of less than 24.29 Å,although it has D6R in its crystal structure, the interaction betweencopper and aluminum constituting the framework of the crystal structureis weak. As a result, aggregation of copper by exposure to a hightemperature/high humidity reducing atmosphere is likely to proceed. As aresult, the hydrocarbon adsorbing properties will remarkably decreaseafter exposure to a high temperature/high humidity reducing atmosphere.With a view to improving thermal stability of the FAU structure, thelattice constant is preferably at most 24.55 Å, more preferably at most24.51 Å, further preferably at most 24.50 Å, particularly preferably atmost 24.48 Å. In one embodiment, the lattice constant is preferably atleast 24.40 Å and at most 24.50 Å, more preferably at least 24.45 Å andat most 24.50 Å.

In the embodiment of the present invention, the lattice constant is avalue measured by the method for measuring the lattice constant of theFAU type zeolite in accordance with ASTM D3942-80.

In the embodiment of the present invention, so long as the FAU typezeolite has the above lattice constant, the molar ratio of silica toalumina (hereinafter sometimes referred to as “SiO₂/Al₂O₃ ratio”) isoptional. Usually, the SiO₂/Al₂O₃ ratio and the lattice constant ofzeolite have a direct correlation with each other. On the other hand, inthe embodiment of the present invention, the SiO₂/Al₂O₃ ratio and thelattice constant of the FAU type zeolite have no direct correlation. Inthe embodiment of the present invention, the SiO₂/Al₂O₃ ratio of the FAUtype zeolite may be at least 1.25 and at most 50.0, and is preferably atleast 3.0 and at most 30.0. As a particularly preferred SiO₂/Al₂O₃ratio, at least 3.0 and at most 25.0 may be mentioned, at least 4.0 andat most 12.0 is preferred, at least 4.5 and at most 9.5 is morepreferred.

In the embodiment of the present invention, the FAU type zeolitecontains copper. As compared with a FAU type zeolite containing copper(hereinafter sometimes referred to as “copper-containing FAU typezeolite”), a FAU type zeolite containing no copper has a remarkably lowhydrocarbon holding power. Most of the hydrocarbons adsorbed in the FAUtype zeolite containing no copper are readily discharged from the FAUtype zeolite. When the FAU type zeolite contains copper, the interactionbetween the hydrocarbons and the FAU type zeolite will be stronger, andthe adsorbed hydrocarbons will hardly be discharged from the FAU typezeolite containing copper.

In the embodiment of the present invention, the state of coppercontained in the FAU type zeolite is preferably bivalent copper (Cu²⁺),more preferably homogeneously dispersed bivalent copper (hereinaftersometimes referred to as “dispersed copper”). The dispersed copper maybe at least either one of Cu²⁺ ion and CuO cluster, and is preferablyCu²⁺ ion.

In the embodiment of the present invention, the state of coppercontained in the FAU type zeolite may be confirmed by a hydrogenconsumption peak accompanying reduction of copper, in H₂-TPRmeasurement. In the H₂-TPR measurement, the bivalent copper is confirmedby a hydrogen consumption peak (hereinafter sometimes referred to as“bivalent copper peak”) with a peak top at a temperature of higher than200° C. and at most 500° C. Further, the dispersed copper such as Cu²⁺ion is confirmed by a hydrogen consumption peak (hereinafter sometimesreferred to as “dispersed copper peak”) with a peak top at a temperatureof at least 300° C. and at most 500° C., and agglomerated bivalentcopper, such as copper oxide (CuO) (hereinafter sometimes referred to as“agglomerated copper”) is confirmed by a hydrogen consumption peak(hereinafter sometimes referred to as “aggregated copper peak”) with apeak top at a temperature of higher than 200° C. and lower than 300° C.Further, monovalent copper is confirmed by a hydrogen consumption peakwith a peak top at a temperature of higher than 500° C.

In the embodiment of the present invention, as the conditions for H₂-TPRmeasurement, the following conditions may be mentioned.

-   -   Measurement atmosphere: 5 vol % hydrogen-containing helium        atmosphere    -   Flow rate: 30 mL/min    -   Temperature-raising rate: 10° C./min    -   Measurement temperature: 50 to 700° C.    -   Sample amount: 0.3 g

In the embodiment of the present invention, the FAU type zeolitepreferably has dispersed copper even after exposed to a high temperaturereducing atmosphere and then exposed to a high temperature oxidizingatmosphere, more preferably has a dispersed copper peak in H₂-TPRmeasurement in a state after subjected to exposure treatment to areducing atmosphere at a temperature of at least 800° C. and at most1,000° C. and then to exposure treatment to an oxidizing atmosphere at atemperature of at least 400° C. and at most 600° C. Particularly, theFAU type zeolite preferably has a dispersed copper peak in H₂-TPRmeasurement after subjected to exposure treatment to a high temperaturereducing atmosphere (hereinafter sometimes referred to as “hightemperature reducing treatment”) and then to an exposure treatment to ahigh temperature oxidizing atmosphere (hereinafter sometimes referred toas “high temperature oxidizing treatment”).

-   -   High temperature reduction treatment:        -   treatment atmosphere: 5 vol % hydrogen-containing helium            flowing atmosphere        -   flow rate: 30 to 100 mL/min        -   treatment temperature: at least 850° C. and at most 950° C.        -   treatment time: at least 10 minutes and at most 1 hour        -   sample amount: 0.2 to 0.4 g    -   High temperature oxidizing treatment:        -   treatment atmosphere: air atmosphere        -   treatment temperature: at least 450° C. and at most 550° C.        -   treatment time: at least 30 minutes and at most 2 hours        -   sample amount: 0.2 to 0.4 g

Presence of the dispersed copper peak after the high temperaturereducing treatment and the high temperature oxidizing treatmentindicates copper being contained in the FAU type zeolite in a highlydispersed state even after such high temperature treatments.

In the embodiment of the present invention, the state of coppercontained in the FAU type zeolite may also be confirmed by an ESRspectrum. For example, as the method for measuring the ESR spectrum, thefollowing conditions may be mentioned.

-   -   Microwave frequency: 9.2 to 9.5 GHz    -   Measurement range: 0 to 1,000 mT    -   Sweep magnetic field width: ±500 mT    -   Magnetic field modulation: 90 to 110 kHz    -   Response: 0.05 to 0.5 sec.    -   Magnetic field sweep time: 1 to 10 min.    -   Microwave output: 0.1 to 5 mW    -   Pretreatment temperature: 300 to 500° C.    -   Pretreatment time: 30 minutes to 5 hours

The double integral intensity (hereinafter sometimes referred to as“spin concentration”) of the ESR spectrum is proportional to theconcentration of isolated bivalent copper present in a sample. A highspin concentration means that a large amount of highly dispersedbivalent copper is contained, and the adsorption amount increases by anincrease of the hydrocarbon adsorption sites.

Further, when a large amount of bivalent copper is contained, thethermal durability tends to be particularly high when the proportion ofthe peak intensity at a magnetic field of at least 260 mT and at most270 mT to the peak intensity at a magnetic field of at least 300 mT andat most 320 mT is within a specific range. The peak at a magnetic fieldof at least 260 mT and at most 270 mT, and the peak at a magnetic fieldof at least 300 mT and at most 320 mT, respectively reflect thedispersed copper which interacts with D6R, and the whole dispersedcopper species.

Accordingly, the proportion of the peak intensity at a magnetic field ofat least 260 mT and at most 270 mT to the peak intensity at a magneticfield of at least 300 mT and at most 320 mT is an index of theproportion of the dispersed copper which interacts with D6R present tothe whole dispersed copper species.

The spin concentration is preferably at least 1.0×10¹⁹ (spins/g), morepreferably at least 1.5×10¹⁹ (spins/g), further preferably at least2.0×10¹⁹ (spins/g).

The proportion of the peak intensity at a magnetic field of at least 260mT and at most 270 mT to the peak intensity at a magnetic field of atleast 300 mT and at most 320 mT is preferably at least 0.25 and at most0.50, more preferably at least 0.30 and at most 0.45, further preferablyat least 0.30 and at most 0.40.

The copper content in the FAU type zeolite is preferably at least 0.5 wt% and at most 4.0 wt %, more preferably at least 1.0 wt % and at most3.0 wt %. In a specific embodiment, the copper content in the FAU typezeolite is preferably at least 1.5 wt % and at most 2.8 wt %. Further,in another embodiment, the copper content in the FAU type zeolite ispreferably at least 1.0 wt % and at most 2.8 wt %, more preferably atleast 1.0 wt % and at most 1.8 wt %.

In the embodiment of the present invention, the copper content in theFAU type zeolite is the weight ratio of copper to the weight of metalscontained in the FAU type zeolite as calculated as oxides. For example,the copper content in a FAU type zeolite containing copper (Cu) and analkali metal (M) can be obtained in accordance with the followingformula.Copper content (wt %)=W′_(Cu)/(W_(Al)+W_(Si)+W_(M)+W_(Cu))×100wherein W′_(Cu) is the copper (Cu) content, W_(Al) is the weight ofaluminum (Al) as calculated as oxide (Al₂O₃), W_(Si) is the weight ofsilicon (Si) as calculated as oxide (SiO₂), W_(M) is the weight of thealkali metal as calculated as oxide (M₂O), and W_(Cu) is the weight ofcopper as calculated as oxide (CuO).

In the embodiment of the present invention, the FAU type zeolite maycontain an alkali metal (that is, the alkali metal content may exceed 0wt %), and the alkali metal content is preferably at most 1.0 wt %,whereby the hydrocarbon adsorbent according to the embodiment of thepresent invention tends to have high hydrocarbon adsorbing propertieseven after exposed to a high temperature/high humidity oxidizingatmosphere. The alkali metal content is preferably at least 0 wt % andat most 0.5 wt %, more preferably at least 0 wt % and at most 0.3 wt %,further preferably at least 0 wt % and at most 0.25 wt %.

In the embodiment of the present invention, the alkali metal containedin the FAU type zeolite may be at least either one of potassium (K) andsodium (Na), and particularly the alkali metal may be sodium.

In the embodiment of the present invention, the alkali metal content isthe weight ratio of the alkali metal as calculated as oxide to theweight of the FAU type zeolite. Potassium and sodium as calculated asoxides are respectively potassium oxide (K₂O) and sodium oxide (Na₂O).

In the embodiment of the present invention, the average crystal size ofthe FAU type zeolite may be at least 0.1 μm, and is preferably at least0.3 μm. The average crystal size of the FAU type zeolite is preferablyat least 0.4 μm, more preferably at least 0.5 μm, whereby thehydrocarbon adsorbing properties after exposed not only to a reducingatmosphere but also to a high temperature/high humidity oxidizingatmosphere tend to be high.

With a view to improving workability such as coating property to theadsorbent carrier, the average crystal size of the FAU type zeolite ispreferably at most 2.5 μm, more preferably at most 1.5 μm, furtherpreferably at most 1.0 μm. In order that high hydrocarbon absorbingproperties after exposed to a high temperature/high humidity atmosphereboth in reducing atmosphere and in oxidizing atmosphere are obtained,the FAU type zeolite preferably has the above lattice constant and anaverage crystal size of at least 0.4 μm and at most 2.0 μm, particularlypreferably at least 0.6 μm and at most 0.9 μm.

In the embodiment of the present invention, the average crystal size isthe average particle size of primary particles. The particle size of aprimary particle is a particle size of a primary particle confirmed in ascanning electron microscope (hereinafter sometimes referred to as“SEM”) image obtained by SEM observation, and the average crystal sizeis the average of the particles sizes of primary particles. The methodof measuring the average crystal size may be a method of selecting from80 to 150 primary particles at random observed at 3,000 to 20,000magnifications, measuring the particle sizes of the primary particlesand taking the average as the average crystal size. To select theprimary particles to measure the particle sizes, one or more SEM imagesmay be employed.

In the embodiment of the present invention, the primary particles of theFAU type zeolite are particles observed as independent particles by SEMobservation at 3,000 to 20,000 magnifications.

In the embodiment of the present invention, the FAU type zeolite has aBET specific surface area of preferably at least 500 m²/g and at most900 m²/g, more preferably at least 600 m²/g and at most 800 m²/g.

In the embodiment of the present invention, the hydrocarbon adsorbentmay contain a binding agent. The binding agent may be at least oneselected from the group consisting of silica, alumina, kaolin,attapulgite, montmorillonite, bentonite, allophane and sepiolite.

In the embodiment of the present invention, the hydrocarbon adsorbentmay be used for a method for adsorbing hydrocarbons, and is preferablyused for a method for adsorbing hydrocarbons in an environment such thatthe hydrocarbon adsorbent is exposed to high temperature, morepreferably used for a method for adsorbing hydrocarbons from an exhaustgas of an internal combustion engine, further preferably used for amethod for adsorbing hydrocarbons from an exhaust gas of an internalcombustion engine of a vehicle.

In the embodiment of the present invention, the hydrocarbon adsorbentmay be used for a method for adsorbing hydrocarbons by a methodcomprising a step of bringing the hydrocarbon adsorbent into contactwith a hydrocarbon-containing gas (hereinafter sometimes referred to as“contact step”).

In the contact step, the shape of the hydrocarbon adsorbent is optional,and may be at least either one of a powder and a formed product.

In a case where the hydrocarbon absorbent is in the form of a powder, aslurry containing the hydrocarbon adsorbent may be applied to asubstrate, which is used as an adsorbing member containing theadsorbent. In a case where the hydrocarbon adsorbent is in the form of aformed product, it may be used in an optional shape formed by anoptional method, for example, at least one selected from the groupconsisting of tumbling granulation, press molding, extrusion, injectionmolding, casting and sheet forming. The shape of the formed product maybe at least one selected from the group consisting of a sphere, asubstantial sphere, an ellipse, a disk, a cylinder, a polyhedron, anindefinite shape and a petal.

The hydrocarbon-containing gas is a gas containing hydrocarbons, and thehydrocarbons may be at least either one of an aliphatic hydrocarbon andan aromatic hydrocarbon, preferably a C₆₋₁₅ hydrocarbon, more preferablyan aromatic hydrocarbon, further preferably at least one selected fromthe group consisting of benzene, toluene and xylene.

The hydrocarbon concentration in the hydrocarbon-containing gas may beat least 0.001 vol % and at most 5 vol % as calculated as methane,preferably at least 0.005 vol % and at most 3 vol %. Thehydrocarbon-containing gas may contain at least one selected from thegroup consisting of carbon monoxide, carbon dioxide, hydrogen, oxygen,nitrogen, nitrogen oxide, sulfur oxide and water.

In the contact step, conditions under which the hydrocarbon adsorbentand the hydrocarbon-containing gas are brought into contact with eachother are optional. As the contact conditions, the following conditionsmay, for example, be mentioned.

-   -   Space velocity: at least 100 hr⁻¹ and at most 500,000 hr⁻¹    -   Contact adsorption: at least −30° C. and at most 200° C.

In the embodiment of the present invention, the hydrocarbon adsorbentmay be produced by an optional method so long as copper is contained inthe FAU type zeolite having a lattice constant of at least 24.29 Å.

In the embodiment of the present invention, as a method for producingthe hydrocarbon adsorbent, a method for producing the hydrocarbonadsorbent may be mentioned, comprising a step of bringing a FAU typezeolite having a lattice constant of at least 24.29 Å and a coppersource into contact with each other (hereinafter sometimes referred toas “metal contacting step”) and a step of calcining the FAU type zeoliteafter the metal contacting step (hereinafter sometimes referred to as“calcining step”).

In the metal contacting step, the lattice constant of the FAU typezeolite may sometimes change by contact with the copper source.Accordingly, the lattice constant of the FAU type zeolite to besubjected to the metal contacting step is preferably at least 24.29 Åand at most 24.60 Å, more preferably at least 24.29 Å and at most 24.57Å.

The copper source is a compound containing copper (Cu), and ispreferably a copper salt, more preferably at least one selected from thegroup consisting of a nitrate, sulfate, acetate, chloride, complex salt,oxide and composite oxide containing copper, further preferably at leastone selected from the group consisting of copper nitrate, copper sulfateand copper acetate.

As the method of bringing the FAU type zeolite and the copper sourceinto contact with each other, a known method may be employed, at leastone selected from the group consisting of ion exchange method,impregnation method, evaporation-to-dryness method, precipitation methodand physical mixing method may be mentioned, at least either one of ionexchange method an impregnation method is preferred, and impregnationmethod is more preferred.

After the FAU type zeolite and the copper source are brought intocontact with each other, the FAU type zeolite may be washed and dried byan optional method. The washing method may be washing with a sufficientamount of water, and the drying method may be treatment in the air atfrom 100° C. to 150° C. for from 5 hours to 30 hours.

The calcining conditions in the calcining step are optional, and thefollowing conditions may be mentioned.

-   -   Calcining atmosphere: in an oxidizing atmosphere, preferably in        the air    -   Calcining temperature: at least 400° C. and at most 600° C.    -   Calcining time: at least 30 minutes and at most 5 hours

The calcining step is carried out preferably in a stream of the air, andthe air in the stream preferably has a low moisture content. Bycalcining in the air having a low moisture content, the interactionbetween copper and aluminum constituting the framework of the crystalstructure tends to be strong, and the thermal durability tends toimprove. The moisture content of the air in the stream is preferably atmost 0.7 vol %, more preferably at most 0.5 vol %, further preferably atmost 0.3 vol %.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples. Reagents,etc. are commercial products unless otherwise specified.

Average Crystal Size

A sample was observed with a general scanning electron microscope(apparatus name: JSM-6390LV, manufactured by JEOL Ltd., hereinafterreferred to as “SEM”) under the following conditions to obtain SEMimages of two fields of view each at magnifications of 5,000 and 15,000,i.e. 4 fields of view in total. 100 Primary particles were selected atrandom from the obtained SEM images, and the average value of thehorizontal Feret's diameters was obtained and taken as the averagecrystal size. Compositional Analysis

A sample was dissolved in a mixed aqueous solution of hydrofluoric acidand nitric acid to prepare a sample solution. The sample solution wasmeasured by means of inductively coupled plasma atomic emissionspectroscopy (ICP-AES) using a general ICP apparatus (apparatus name:OPTIMA5300DV, manufactured by PerkinElmer), and the composition wasdetermined from the obtained measured values of the respective elements.

Measurement of Hydrocarbon Adsorption Ratio

The hydrocarbon adsorbent was pressure-formed, crushed and formed intoagglomerated particles having an agglomerate size of from 20 to 30 mesh.0.1 g of the agglomerated particles was filled in a normal pressurefixed bed flow reactor, treated in a stream of nitrogen at 500° C. forone hour and cooled to 50° C. to conduct pretreatment. Ahydrocarbon-containing gas was made to flow through the hydrocarbonadsorbent after the pretreatment to measure the hydrocarbon adsorptionratio.

The composition of the hydrocarbon-containing gas and the conditions forthe hydrocarbon adsorption measurement are shown below.

Hydrocarbon-containing toluene 3,000 vol ppmC gas: (concentration ascalculated as methane) oxygen 1 vol % water 3 vol % nitrogen the restGas flow rate: 200 mL/min Temperature-raising rate: 10° C./minMeasurement temperature: 50 to 200° C. Measurement time: 15 minutes

Using a flame ionization detector (FID), the hydrocarbons in the gasafter made to flow through the hydrocarbon adsorbent were continuouslyquantitatively analyzed. The hydrocarbon concentration of thehydrocarbon-containing gas on the inlet side of the normal pressurefixed bed flow reactor (concentration as calculated as methane,hereinafter referred to as “inlet concentration”) and the hydrocarbonconcentration of the hydrocarbon-containing gas on the outlet side ofthe normal pressure fixed bed flow reactor (concentration as calculatedas methane, hereinafter referred to as “outlet concentration”) weremeasured.

The ratio of the integral value of the outlet concentration(concentration as calculated as methane) to the integral value of theinlet concentration was obtained as the hydrocarbon adsorption ratio.

Reduction Hydrothermal Durability Treatment

The hydrocarbon adsorbent was treated in the same manner as (measurementof hydrocarbon adsorption ratio) except that a treatment gas was made toflow through the hydrocarbon adsorbent after the pretreatment under thefollowing conditions to conduct reduction hydrothermal durabilitytreatment.

Treatment gas: propylene 3,000 vol ppmC (concentration as calculated asmethane) water 10 vol % nitrogen the rest Gas flow rate: 300 mL/minSpace velocity: 6,000 hr⁻¹ Treatment temperature: 900° C. Treatmenttime: 2 hours

Oxidation Hydrothermal Durability Treatment

The hydrocarbon adsorbent was treated in the same manner as (measurementof hydrocarbon adsorption ratio) except that a treatment gas was made toflow through the hydrocarbon adsorbent after the pretreatment under thefollowing conditions to conduct oxidation hydrothermal durabilitytreatment.

Treatment gas: water 10 vol % nitrogen the rest Gas flow rate: 300mL/min Space velocity: 6,000 hr⁻¹ Treatment temperature: 900° C.Treatment time: 2 hours

Example 1

10 g of a FAU type zeolite having a lattice constant of 24.53 Å and 4.58g of an aqueous copper nitrate solution (containing 0.58 g of coppernitrate trihydrate) were mixed and dried in the air at 110° C. forovernight. The FAU type zeolite after drying was calcined in a stream ofair having a moisture content of 0.1 vol % at 550° C. for 2 hours toobtain a copper-containing FAU type zeolite, which was taken as thehydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.49 Å, a SiO₂/Al₂O₃ ratio of 7.4, a copper content of 1.51 wt %, asodium content of 0.09 wt % and an average crystal size of 0.81 μm.

Example 2

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.31 Å was used, which was taken as the hydrocarbon adsorbent in thisExample.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.31 Å, a SiO₂/Al₂O₃ ratio of 29.0, a copper content of 1.59 wt %, asodium content of 0.12 wt % and an average crystal size of 0.71 μm.

Example 3

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.52 Å was used and that 4.98 g of an aqueous copper nitrate solution(containing 0.98 g of copper nitrate trihydrate) was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.48 Å, a SiO₂/Al₂O₃ ratio of 7.1, a copper content of 2.62 wt %, asodium content of 0.09 wt % and an average crystal size of 0.75 μm.

Example 4

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.52 Å was used and that 4.38 g of an aqueous copper nitrate solution(containing 0.38 g of copper nitrate trihydrate) was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.47 Å, a SiO₂/Al₂O₃ ratio of 7.1, a copper content of 1.02 wt %, asodium content of 0.09 wt % and an average crystal size of 0.75 μm.

Example 5

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that 5.16 g of an aqueous copper nitrate solution(containing 1.16 g of copper nitrate trihydrate) was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing zeolite had a lattice constant of 24.49Å, a SiO₂/Al₂O₃ ratio of 7.4, a copper content of 2.99 wt %, a sodiumcontent of 0.09 wt % and an average crystal size of 0.81 μm.

Example 6

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.48 Å was used, which was taken as the hydrocarbon adsorbent in thisExample.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.43 Å, a SiO₂/Al₂O₃ ratio of 6.1, a copper content of 1.56 wt %, asodium content of 0.24 wt % and an average crystal size of 0.75 μm.

Example 7

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.48 Å was used, which was taken as the hydrocarbon adsorbent in thisExample.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.46 Å, a SiO₂/Al₂O₃ ratio of 5.4, a copper content of 1.59 wt %, asodium content of 4.02 wt % and an average crystal size of 0.36 μm.

Example 8

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.37 Å was used, which was taken as the hydrocarbon adsorbent in thisExample.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.34 Å, a SiO₂/Al₂O₃ ratio of 6.0, a copper content of 1.59 wt %, asodium content of 0.30 wt % and an average crystal size of 0.36 μm.

Example 9

50 g of a FAU type zeolite having a lattice constant of 24.63 Å wasion-exchanged with 125 g of an aqueous 20% ammonium chloride solution,washed with 1 L of pure water and dried at 110° C. overnight. The driedpowder was calcined in a 60 vol % water-containing air at 600° C. for 4hours. 20 g of the calcined powder was put into 100 g of 1.6%hydrochloric acid and subjected to heat treatment at 60° C. for onehour. Then, the powder was washed with 1 L of pure water and furtherion-exchanged with 600 g of 20% ammonium chloride and washed with 1 L ofpure water to obtain a FAU type zeolite of 24.55 Å.

A copper-containing FAU type zeolite was obtained in the same manner asin Example 3 except that the above FAU type zeolite was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.51 Å, a SiO₂/Al₂O₃ ratio of 7.0, a copper content of 2.51 wt %, asodium content of 0.29 wt % and an average crystal size of 0.75 μm.

Example 10

50 g of a FAU type zeolite having a lattice constant of 24.63 Å wasion-exchanged with 125 g of an aqueous 10% ammonium chloride solution,washed with 1 L of pure water and dried at 110° C. overnight. The driedpowder was calcined in a 60 vol % water-containing air at 740° C. for 2hours. 20 g of the calcined powder was put into 100 g of 1.6%hydrochloric acid and subjected to heat treatment at 60° C. for onehour. Then, the powder was washed with 1 L of pure water to obtain a FAUtype zeolite of 24.50 Å.

A copper-containing FAU type zeolite was obtained in the same manner asin Example 3 except that the above FAU type zeolite was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.48 Å, a SiO₂/Al₂O₃ ratio of 6.1, a copper content of 2.47 wt %, asodium content of 0.73 wt % and an average crystal size of 0.75 μm.

Example 11

50 g of a FAU type zeolite having a lattice constant of 24.63 Å wasion-exchanged with 50 g of an aqueous 10% ammonium chloride solution,washed with 1 L of pure water and dried at 110° C. overnight. The driedpowder was calcined in a 60 vol % water-containing air at 600° C. for 4hours. 20 g of the calcined powder was put into 100 g of 1.6%hydrochloric acid and subjected to heat treatment at 60° C. for onehour. Then, the powder was washed with 1 L of pure water and furtherion-exchanged with 600 g of 20% ammonium chloride and washed with 1 L ofpure water to obtain a FAU type zeolite of 24.60 Å.

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that the above FAU type zeolite was used, and that4.98 g of an aqueous copper nitrate solution (containing 0.98 g ofcopper nitrate trihydrate) was used, which was taken as the hydrocarbonadsorbent in this Example.

[0085]

The obtained copper-containing FAU type zeolite had a lattice constantof 24.52 Å, a SiO₂/Al₂O₃ ratio of 7.1, a copper content of 2.50 wt %, asodium content of 0.57 wt % and an average crystal size of 0.75 μm.

Example 12

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.52 Å was used and that 6.00 g of an aqueous copper nitrate solution(containing 2.00 g of copper nitrate trihydrate) was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.50 Å, a SiO₂/Al₂O₃ ratio of 7.1, a copper content of 4.73 wt %, asodium content of 0.09 wt % and an average crystal size of 0.75 μm.

Comparative Example 1

A FAU type zeolite having a lattice constant of 24.53 Å was used as thehydrocarbon adsorbent in this Comparative Example. The copper-containingFAU type zeolite had a lattice constant of 24.53 Å, a SiO₂/Al₂O₃ ratioof 7.4, a copper content of 0 wt %, a sodium content of 0.09 wt % and anaverage crystal size of 0.81 μm.

Comparative Example 2

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.25 Å was used, which was taken as the hydrocarbon adsorbent in thisComparative Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.25 Å, a SiO₂/Al₂O₃ ratio of 14.9, a copper content of 1.57 wt %, asodium content being the detection limit or lower and an average crystalsize of 0.38 μm.

Comparative Example 3

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.28 Å was used, which was taken as the hydrocarbon adsorbent in thisComparative Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.27 Å, a SiO₂/Al₂O₃ ratio of 28.0, a copper content of 1.60 wt %, asodium content of 0.10 wt % and an average crystal size of 0.60 μm.

Comparative Example 4

A copper-containing MFI type zeolite was obtained in the same manner asin Example 1 except that a MFI type zeolite was used and that 4.58 g ofan aqueous copper nitrate solution (containing 0.58 g of copper nitratetrihydrate) was used, which was taken as the hydrocarbon adsorbent inthis Comparative Example.

The obtained copper-containing MFI type zeolite had a SiO₂/Al₂O₃ ratioof 38, a copper content of 1.52 wt % and a sodium content of 0.02 wt %.

Comparative Example 5

A copper-containing BEA type zeolite was obtained in the same manner asin Example 1 except that a BEA type zeolite was used and that 4.58 g ofan aqueous copper nitrate solution (containing 0.58 g of copper nitratetrihydrate) was used, which was taken as the hydrocarbon adsorbent inthis Comparative Example.

The obtained copper-containing BEA type zeolite had a SiO₂/Al₂O₃ ratioof 40, a copper content of 1.47 wt % and a sodium content of 0.04 wt %.

Comparative Example 6

15 g of a MFI type zeolite was added to 135 g of an aqueous silvernitrate solution (silver nitrate concentration: 3.2 wt %) followed bymixing with stirring at 60° C. overnight to ion-exchange the zeolite.The ion-exchanged MFI type zeolite was subjected to filtration, washedand dried in the air at 110° C. overnight to obtain a silver-containingMFI type zeolite, which was taken as the hydrocarbon adsorbent in thisComparative Example.

The obtained silver-containing MFI type zeolite had a SiO₂/Al₂O₃ ratioof 38.0, a silver content of 4.50 wt % and a sodium content being thedetection limit or lower.

Comparative Example 7

A copper-containing FAU type zeolite was obtained in the same manner asin Example 1 except that a FAU type zeolite having a lattice constant of24.26 Å was used and that 4.98 g of an aqueous copper nitrate solution(containing 0.98 g of copper nitrate trihydrate) was used, which wastaken as the hydrocarbon adsorbent in this Example.

The obtained copper-containing FAU type zeolite had a lattice constantof 24.26 Å, a SiO₂/Al₂O₃ ratio of 103, a copper content of 2.53 wt %, asodium content of 0.09 wt % and an average crystal size of 0.77 μm.

Measurement Example 1

The hydrocarbon adsorbent in each of Examples 1 and 2 and ComparativeExamples 1 to 3 was subjected to reduction hydrothermal durabilitytreatment. The hydrocarbon adsorption ratio of each hydrocarbonadsorbent after the reduction hydrothermal durability treatment wasmeasured. The results are shown in the following Table.

TABLE 1 Lattice Hydrocarbon constant SiO₂/Al₂O₃ Copper contentadsorption ratio (Å) ratio (wt %) (%) Example 1 24.49 7.4 1.51 46Example 2 24.31 29.0 1.59 46 Comparative 24.52 7.4 0 3 Example 1Comparative 24.25 14.9 1.57 11 Example 2 Comparative 24.28 28.0 1.60 17Example 3

It was confirmed from Example 1 and Comparative Example 1 that thehydrocarbon adsorption ratio of the hydrocarbon adsorbent containing nocopper is remarkably low.

The hydrocarbon adsorbents in Examples 1 and 2 and Comparative Examples2 and 3 contain copper at the same level. However, it is confirmed thatthe hydrocarbon adsorbents in Examples 1 and 2 with a lattice constantof at least 24.31 Å have a remarkably high hydrocarbon adsorption ratioas compared with the hydrocarbon adsorbents in Comparative Examples 2and 3 with a lattice constant of less than 24.29 Å.

Of the hydrocarbon adsorbents containing copper, the relation betweenthe lattice constant and the hydrocarbon adsorption ratio is shown inFIG. 1 , and the relation between the SiO₂/Al₂O₃ ratio and thehydrocarbon adsorption ratio is shown in FIG. 2 . It is confirmed fromFIG. 1 that the hydrocarbon adsorption ratio is remarkably high when thelattice constant is at least 24.29 Å. Further, no correlation betweenthe SiO₂/Al₂O₃ ratio and the hydrocarbon adsorption ratio is confirmedfrom FIG. 2 .

Measurement Example 2

The hydrocarbon adsorbent in each of Examples 3 to 5 and 12 wassubjected to reduction hydrothermal durability treatment. Thehydrocarbon adsorption ratio of each hydrocarbon adsorbent after thereduction hydrothermal durability treatment was measured. The resultsare shown in the following Table and FIG. 3 together with the results inExample 1 in Measurement Example 1.

TABLE 2 Lattice Hydrocarbon constant SiO₂/Al₂O₃ Copper contentadsorption ratio (Å) ratio (wt %) (%) Example 1 24.49 7.4 1.51 46Example 3 24.48 7.1 2.62 62 Example 4 24.47 7.1 1.09 32 Example 5 24.497.4 2.99 63 Example 12 24.50 7.1 4.73 82

It is confirmed from this Measurement Example that the hydrocarbonadsorption ratio after the reduction hydrothermal durability treatmenttends to be high as the copper content increases.

Measurement Example 3

The hydrocarbon adsorbent in each of Examples 6 to 8 was subjected toreduction hydrothermal durability treatment. The hydrocarbon adsorptionratio of each hydrocarbon adsorbent after the reduction hydrothermaldurability treatment was measured. The results are shown in thefollowing Table together with the results in Comparative Example 3 inMeasurement Example 1.

TABLE 3 Lattice Copper Average Sodium Hydrocarbon constant contentcrystal size content adsorption ratio (Å) (wt %) (μm) (wt %) (%) Example6 24.43 1.56 0.75 0.24 47 Example 7 24.46 1.59 0.36 4.02 32 Example 824.34 1.59 0.36 0.30 42 Comparative 24.28 1.60 0.60 0.10 17 Example 3

It is confirmed from this Measurement Example that the hydrocarbonadsorption ratio tends to decrease as the average crystal size becomessmaller and as the sodium content increases. However, it is confirmedthat the hydrocarbon adsorbent in each Example has a high hydrocarbonadsorption ratio as compared with the hydrocarbon adsorbent inComparative Example 3 with a lattice constant of less than 24.29 Å.

Measurement Example 4

The hydrocarbon adsorbent in each of Comparative Examples 4 to 6 wassubjected to reduction hydrothermal durability treatment. Thehydrocarbon adsorption ratio of each hydrocarbon adsorbent after thereduction hydrothermal durability treatment was measured. The resultsare shown in the following Table together with the results in Example 4in Measurement Example 1.

TABLE 4 Crystal Metal Hydrocarbon structure Metal species contentadsorption ratio (Å) contained (wt %) (%) Example 4 FAU Cu 1.02 35Comparative MFI Cu 1.52 0 Example 4 Comparative BEA Cu 1.47 8 Example 5Comparative MFI Ag 4.50 13 Example 6

It is confirmed that the hydrocarbon adsorbent in Example 4 has aremarkably high hydrocarbon adsorption ratio although it has a low metalcontent, as compared with the BEA type zeolite and the MFI type zeolitewhich have been used as conventional hydrocarbon adsorbents.

Measurement Example 5

The hydrocarbon adsorbent in each of Examples 1, 2, 3, 6 and 8 andComparative Examples 3 and 6 was subjected to oxidation hydrothermaldurability treatment. The hydrocarbon adsorption ratio of eachhydrocarbon adsorbent after the oxidation hydrothermal durabilitytreatment was measured. The results are shown in the following Table.

TABLE 5 Hydrocarbon Lattice Metal Metal Average adsorption constantspecies content crystal size ratio (Å) contained (wt %) (μm) (%) Example1 24.49 Cu 1.51 0.81 47 Example 2 24.31 Cu 1.59 0.71 32 Example 3 24.48Cu 2.62 0.75 60 Example 6 24.43 Cu 1.56 0.75 37 Example 8 24.34 Cu 1.590.36 18 Comparative 24.28 Cu 1.60 0.60 9 Example 3 Comparative — Ag 4.50— 26 Example 6

It is confirmed from this Measurement Example that regarding thehydrocarbon adsorbents containing copper, the hydrocarbon adsorbenthaving a lattice constant of at least 24.29 Å has a high hydrocarbonadsorption ratio after the oxidation hydrothermal durability treatmentas compared with the hydrocarbon adsorbent having a lattice constant ofless than 24.29 Å. Further, it is confirmed from Example 8 andComparative Example 3 that the hydrocarbon adsorbent having a latticeconstant of at least 24.29 Å, even having a small average particle size,has a high hydrocarbon adsorption ratio after the oxidation hydrothermaldurability treatment as compared with the FAU type zeolite having alattice constant of less than 24.29 Å.

Further, it is confirmed that even as compared with the conventionalhydrocarbon adsorbent in Comparative Example 6, the hydrocarbonadsorbent having a larger average crystal size than the hydrocarbonadsorbent in Example 8 has a high hydrocarbon adsorption ratio after theoxidation hydrothermal durability treatment.

Measurement Example 6

The hydrocarbon adsorbent in each of Examples 9, 10 and 11 was subjectedto oxidation hydrothermal durability treatment. The hydrocarbonadsorption ratio of each hydrocarbon adsorbent after the oxidationhydrothermal durability treatment was measured. The results are shown inthe following Table.

TABLE 6 Lattice Copper Average Sodium Hydrocarbon constant contentcrystal size content adsorption ratio (Å) (wt %) (μm) (wt %) (%) Example9 24.51 2.51 0.75 0.29 43 Example 10 24.48 2.47 0.75 0.73 45 Example 1124.52 2.50 0.71 0.57 0

It is confirmed from Examples 9 and 11 in this Measurement Example thatthe hydrocarbon adsorbent having a lattice constant of at most 24.51 Åhas a high hydrocarbon adsorption ratio after the oxidation hydrothermaldurability treatment.

Measurement Example 7

The hydrocarbon adsorbent in each of Example 1 and Comparative Example 3was pressure-formed, crushed and formed into agglomerated particleshaving an agglomerate size of from 12 to 20 mesh. 0.3 g of each of theagglomerated particles was weighed, subjected to high temperaturereduction treatment and then subjected to high temperature oxidationtreatment. The conditions for the high temperature reduction treatmentand the high temperature oxidation treatment are as follows.

High temperature reduction treatment: treatment atmosphere 5 vol %hydrogen-containing helium atmosphere treatment temperature 900° C.treatment time 0.5 hour High temperature oxidation treatment: treatmentatmosphere air atmosphere treatment temperature 500° C. treatment time 1hour

Each hydrocarbon adsorbent after the treatments was subjected topretreatment and then subjected to H₂-TPR measurement. The pretreatmentand H₂-TPR conditions are shown below, the results in Example 1 areshown in FIG. 4 , and the results in Comparative Example 3 are shown inFIG. 5 .

Pretreatment: atmosphere helium atmosphere treatment temperature 300° C.treatment time 0.5 hour H₂-TPR: atmosphere 5 vol % hydrogen-containingair temperature-raising rate 10° C./hr measurement temperature 100° C.to 700° C.

From FIGS. 4 and 5 , a hydrogen consumption peak with a peak top in thevicinity of 400° C. is confirmed for the hydrocarbon absorbent inExample 1 after subjected to the high temperature reduction treatmentand the high temperature oxidation treatment, whereas no hydrogenconsumption peak with a peak top at 300° C. or higher was confirmed forthe hydrocarbon adsorbent in Comparative Example 3.

Measurement Example 8

The hydrocarbon adsorbent in each of Examples 1, 3, 5 and 12 andComparative Example 7 was subjected to ESR measurement under thefollowing conditions.

-   -   Measurement apparatus: manufactured by JEOL Ltd., JES-TE200    -   Microwave frequency: 9.4 GHz    -   Measurement range: 200 to 400 mT    -   Magnetic field modulation: 100 kHz    -   Response: 0.3 sec.    -   Magnetic field sweep time: 4 min.    -   Microwave output: 1.0 mW

As a sample (hydrocarbon adsorbent), 10 mg of a powder was filled in aquartz tube having a diameter of 5 mm and dried at 400° C. for 5 hours,and the tube was sealed.

The ESR spectrum of Example 3 obtained by the ESR measurement is shownin FIG. 6 .

The spin concentration was obtained by double integration at a magneticfield within a range of from 220 to 380 mT by analysis softwareES-IPRITS DATA SYSTEM version 6.2.

From the obtained ESR spectrum, the ratio of the peak intensity at amagnetic field at least 260 mT and at most 270 mT to the peak intensityat a magnetic field of at least 300 mT and at most 320 mT wascalculated. In the following, the peak at a magnetic field of at least260 mT and at most 270 mT will sometimes be referred to as “peak 1”, thepeak at a magnetic field of at least 300 mT and at most 320 mT as “peak2”, and the ratio of the peak intensity at a magnetic field of at least260 mT and at most 270 mT to the peak intensity at a magnetic field ofat least 300 mT and at most 320 mT as “peak 1/peak 2 intensity ratio”.

TABLE 7 Hydrocarbon Spin Peak 1/ adsorption ratio Copper concen- peak 2after hydrothermal content tration intensity durability treatment (wt %)(spin/g) ratio (%) Example 1 1.51 9.2 × 10¹⁹ 0.42 43 Example 3 2.62 1.1× 10²⁰ 0.35 60 Example 5 2.99 2.1 × 10¹⁹ 0.26 23 Example 12 4.73 4.6 ×10²⁰ 0.10 0 Comparative 2.50 1.2 × 10¹⁸ Peak 1 0 Example 7 not confirmed

From comparison between Examples 1, 3 and 5, and Example 12 andComparative Example 7, in this Measurement Example, the hydrocarbonadsorption ratio after the oxidation hydrothermal durability treatmentis high when the spin concentration is at least 1.0×10¹⁹ (spins/g) andthe peak 1/peak 2 intensity ratio is at least 0.25 and at most 0.50.

The present invention has been described in detail with reference tospecific embodiments, but, it is obvious for the person skilled in theart that various changes and modifications are possible withoutdeparting from the intention and the scope of the present invention.

The entire disclosure of Japanese Patent Application No. 2018-037603filed on Mar. 2, 2018 including specification, claims, drawings andsummary is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The hydrocarbon adsorbent of the present invention may be used for amethod for adsorbing hydrocarbons to be exposed to a hightemperature/high humidity environment, and may be used particularly fora method for adsorbing hydrocarbons in an exhaust gas in an internalcombustion engine, such as an automobile exhaust gas.

The invention claimed is:
 1. A hydrocarbon adsorbent, which comprisesFAU type zeolite having a lattice constant of at least 24.29 Å and atmost 24.51 Å and containing bivalent copper.
 2. The hydrocarbonadsorbent according to claim 1, wherein the FAU type zeolite has anaverage crystal size of at least 0.45 μm.
 3. The hydrocarbon adsorbentaccording to claim 1, wherein the FAU type zeolite has a copper contentof at least 0.5 wt % and at most 4.0 wt %.
 4. The hydrocarbon adsorbentaccording to claim 1, wherein the FAU type zeolite has an alkali metalcontent as calculated as oxides of at most 1 wt %.
 5. The hydrocarbonadsorbent according to claim 1, wherein the FAU type zeolite has ahydrogen consumption peak with a peak top at a temperature of at least300° C. and at most 500° C., in H₂-TRP measurement in a state aftersubjected to exposure treatment to a reducing atmosphere at atemperature of at least 800° C. and at most 1,000° C. and then toexposure treatment to an oxidizing atmosphere at a temperature of atleast 400° C. and at most 600° C.
 6. The hydrocarbon adsorbent accordingto claim 1, wherein the FAU type zeolite has, in ESR measurement, a spinconcentration of a least 1.0×10¹⁹ (spins/g) and a ratio of a peakintensity at a magnetic field of at least 260 mT and at most 270 mT to apeak intensity at a magnetic field of at least 300 mT and at most 320 mTof at least 0.25 and at most 0.50.
 7. A method for treating ahydrocarbon-containing gas comprising contacting ahydrocarbon-containing gas with the hydrocarbon adsorbent as defined inclaim 1.